The primary focus of this report is to present a georeferenced, digital sidescan-sonar mosaic of the study region. The sidescan-sonar data were acquired with the AMS-120 (120kHz) sidescan-sonar system during USGS cruise F9-89-NC. The dataset covers approximately 1000 km² of the continental shelf between Point Reyes, California and Half Moon Bay, California, extending west to the continental shelf break near the Farallon Islands. The sidescan-sonar mosaic displays a heterogenous sea-floor environment, containing outcropping rock, ripples, dunes, lineations and depressions, as well as flat, featureless sea floor (Karl and others, 2002). These data, along with sub-bottom interpretation and ground truth data define the geologic framework of the region. The sidescan-sonar mosaic can be used with supplemental remote sensing and sampling data as a base for future research, helping to define the local current regime and predominant sediment transport directions and forcing conditions within the Gulf of Farallones.
Sweeney, Edward M. , 2004, 500 meter bathymetric contours: U.S. Geological Survey, Woods Hole, MA.This is part of the following larger work.Online Links:
Sweeney, Edward M. , Danforth, William W. , Karl, Herman A. , O'Brien, Thomas F. , and Schwab, William C. , 2004, The Gulf of Farallones: Sidescan-Sonar Imagery: Open-File Report 2004-1082, U.S. Geological Survey, U.S. Geological Survey, Woods Hole Science Center, Woods Hole, MA.Online Links:
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000089992. Longitudes are given to the nearest 0.000089992. Latitude and longitude values are specified in Decimal degrees.
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257224.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
Identification number generated internally.
| Range of values | |
|---|---|
| Minimum: | -2500 |
| Maximum: | -200 |
| Units: | meters |
(508) 548-8700 x2307 (voice)
(508) 457-2310 (FAX)
esweeney@usgs.gov
The 500m contour ESRI vector shapefile serves as continental shelf bathymetric reference information for GIS mapping and the viewing of the Gulf of the Farallones sidescan-sonar data set.
National Geophysical Data Center (NGDC), 2001, Coastal Relief Model, Central Pacific Coast, Vol 7.
Person who carried out this activity:
(508) 548-8700 x2307 (voice)
(508) 457-2310 (FAX)
esweeney@usgs.gov
These data were generated from an ESRI grid of the NGCD Coastal Relief Model. The accuracy of these data are inherited from the Coastal Relief Model.
Soundings for each volume of the Coastal Relief model series are compiled from hydrographic surveys conducted by the National Ocean Service (NOS) and from various academic institutions. The surveys were carried out using a variety of sounding methods including SeaBeam 16-beam, 12-kHz swath mapping system (6000- >3000m operating water depths), General Instruments 17-beam, 36-kHz Hydrochart II swath mapping system (5-150m operating water depths), single-beam echosounder (e.g., 3.5 kHz narrow 2 degree beam), and lead-line sounding method. These latter surveys date as far back as the late 1800's.
A wide range of navigation methods are also associated with the surveys. Visual navigation is based on three-point sextant fixes, theodolite intersections, and celestial fixes. Electronic navigation involves short to long range positioning systems that run the gamut from Loran-C (0.25 - 5 nm accuracy) to differential GPS (1 m accuracy).
Despite the varying sounding and navigation techniques upon which they are based, all of the NOS soundings used in constructing the Coastal Relief Model meet rigorous standards for accuracy. The same standards are employed by the International Hydrographic Office and have remained relatively consistent since the 1800's. The vertical accuracy of the soundings
The horizontal accuracy of the soundings is generally 30 m, but it can vary from as fine as 15 m in ports and estuaries to as coarse as 75 m in the offshore areas. Differential GPS has improved this level of accuracy considerably for the most recent survey data.
These data are complete (see: <http://www.ngdc.noaa.gov/mgg/coastal/model.html>)
Land elevations within the gridded dataset come from the United States Geological Survey/ National Image Mapping Agency (USGS/NIMA) 1:250,000 or 1 degree DEMs of the states. A description of the USGS/NIMA DEMs and how they were derived can be accessed on the World Wide Web at <http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_dem>. Our focus, however, is on the bathymetric soundings that are used in constructing the offshore regions of the grids.
Soundings for each volume of the Coastal Relief model series are compiled from hydrographic surveys conducted by the National Ocean Service (NOS) and from various academic institutions. The surveys were carried out using a variety of sounding methods including SeaBeam 16-beam, 12-kHz swath mapping system (6000- >3000m operating water depths), General Instruments 17-beam, 36-kHz Hydrochart II swath mapping system (5-150m operating water depths), single-beam echosounder (e.g., 3.5 kHz narrow 2 degree beam), and lead-line sounding method. These latter surveys date as far back as the late 1800's.
A wide range of navigation methods are also associated with the surveys. Visual navigation is based on three-point sextant fixes, theodolite intersections, and celestial fixes. Electronic navigation involves short to long range positioning systems that run the gamut from Loran-C (0.25 - 5 nm accuracy) to differential GPS (1 m accuracy).
Despite the varying sounding and navigation techniques upon which they are based, all of the NOS soundings used in constructing the Coastal Relief Model meet rigorous standards for accuracy. The same standards are employed by the International Hydrographic Office and have remained relatively consistent since the 1800's. The vertical accuracy of the soundings is 0.3 m in 0 - 20 m of water, 1.0 m in 20 - 100 m of water, and 1% of the water depth in 100 m of water. The horizontal accuracy of the soundings is within a radius of 1.5 mm of the sounding location at the scale at which the soundings are recorded. NOS surveys are plotted at map scales that range from 1/10,000 for harbors and channels to 1/50,000 for open ocean surveys, with 1/20,000 being the most commonly used scale. The horizontal accuracy of the soundings is generally 30 m, but it can vary from as fine as 15 m in ports and estuaries to as coarse as 75 m in the offshore areas. Differential GPS has improved this level of accuracy considerably for the most recent survey data.
While the NOS soundings collected since 1965 have been recorded digitally, those collected prior to this time were recorded manually and then used to make hand-drawn bathymetric maps. Approximately 1,550 of these hand-drawn bathymetric maps have been digitized and assimilated into the NOS Hydrographic Database and, subsequently, were used in constructing the many volumes of the gridded dataset.
Are there legal restrictions on access or use of the data?
- Access_Constraints: None
- Use_Constraints:
- Public domain data from the U.S. government is freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of this dataset.
(508) 548-8700 x2275 (voice)
(580)457-2313 (FAX)
nsoderberg@usgs.gov
500 meter contours (ESRI Shapefile)
Although this data set and its lineage have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data or its related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related items. Users must assume responsibility for the proper use of these data. The data should not be used at resolutions for which they are not intended. The data have not been reviewed for conformity with U.S. Geological Survey editorial standards, or the North American Strigraphic code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government.
| Data format: | 500 meter contours - vectors in format 500mcontours.shp (version ArcGIS 8.3) Size: 0.219 |
|---|
(508) 548-8700 x2307 (voice)
(508) 457-2310 (FAX)
esweeney@usgs.gov